The Mysterious Fate of White Dwarves

 

    This week I would like to bring attention to White Dwarfs on the H-R diagram.  Seen on the bottom-left of the diagram, this class contains the oldest stars in the universe (Redd, 2018).  They are what remains after small-medium sized stars burn off their hydrogen.  The most massive stars never become them- instead they explode into supernova, or become neutron stars or black holes.
    White dwarfs used to be main sequence stars that grew into red giants.  Once their fuel was burned off, the red giants collapsed, leaving behind planetary nebulae, with the much smaller white dwarfs remaining at the center.  Most white dwarfs have a mass similar to our Sun, but since they are much smaller they have a lot more density.  The only objects in space that are denser than white dwarfs are neutron stars and black holes (Redd, 2018).    

    Most white dwarfs are thought to keep expending energy until they turn into what are aptly called black dwarfs.  No black dwarfs have been discovered yet, because it takes trillions of years for white dwarfs to dim by that much.  It's thought that our own Sun will become a red giant, then a white dwarf, and decay for 10 trillion years before it becomes a black dwarf (Klesman, 2020).  However, there are some white dwarfs that are binary, meaning they orbit each other.  When these pairs collide, they are predicted to create either a neutron star or a supernova.
    You have to wonder if the universe will even exist long enough for black dwarfs to make an appearance.  It's difficult to imagine what it will look like in 10 trillion years!

 
Sources:
Redd, Nola Taylor.  2018.  White Dwarfs: Compact Corpses of Stars.  Space.com.  Retrieved from:  https://www.space.com/23756-white-dwarf-stars.html
Klesman, Alison.  2020.  When Will the Sun Become a Black Dwarf?  Astronomy.com.  Retrieved from:  https://astronomy.com/magazine/ask-astro/2020/04/when-will-the-sun-become-a-black-dwarf